A satellite communication system includes a central earth station (often referred to as a hub), a plurality of other earth stations (often referred to as terminals) and a satellite. The hub and the terminals communicate over the satellite using a segment of the satellite's resources (often referred to as space segment), wherein said segment is characterized by its bandwidth and by an amount of transmission power. In order to use the space segment, the hub and the terminals use an access scheme.
In some systems, the hub transmits towards the terminals over a dedicated channel to which all terminals listen (often referred to as the forward channel), while the terminals transmit towards the hub over one or more channels (often referred to as return channel(s)). Use of the return channels is often governed by said access scheme.
Some systems use access schemes in which the terminals transmit in bursts. Such access schemes are often known as Time Division Multiple Access (TDMA) or Multi-Frequency Time Division Multiple Access (MF-TDMA). A terminal having data to transmit towards the hub either selects a channel and a time for transmitting or it is assigned (by the hub) a channel and a time for transmitting. As each physical channel can be occupied at different times by carriers emitted by different terminals, such access schemes allow multiplicity of terminals to share the return channels.
Other systems use access schemes in which the terminals transmit continuous carriers. Such access schemes are often known as Single Channel per Carrier (SCPC). Each terminal uses a dedicated channel and transmits its carrier over the channel without interruptions regardless of whether it has data to transmit or not. In such access schemes, a channel cannot be shared between terminals.
Due to allowing multiplicity of terminals to share the return channels, and due to the terminal using or being assigned capacity over the return channels only when that capacity is needed for transmitting data, MF-TDMA access schemes also allow dimensioning (also referred to as sizing) of the space segment associated with the return channels using a Demand Assignment Multiple Access (DAMA) technique. In a DAMA technique, it is assumed that only some, yet not all, of the terminals simultaneously transmit data, hence the number of return channels needed is lower than the number of terminals in the system.
In SCPC access schemes, each terminal transmits its carrier signal continuously, thus utilizing the satellite's resources (i.e. bandwidth and transmission power) at all times. Such an access scheme does not allow dimensioning of the space segment using a DAMA technique and requires the space segment to support (both in bandwidth and in transmission power) as many channels as the number of terminals in the system.
References to methods for enforcing a total power limit in a satellite communication system may be found in U.S. patent application Ser. No. 12/773,237 (US2010/0284325), entitled “Elastic Access Scheme for Two-Way Satellite Communication Systems” to Yabo et al.
References to methods for managing power in a satellite communication system may be found in U.S. patent application Ser. No. 12/920,616 (US2011/0021137), entitled “Method and Apparatus for Compensation for Weather-Based Attenuation in a Satellite Link” to Laufer.